Genetic polymorphism in MDR-1: a tool for examining allelic expression in normal cells, unselected and drug-selected cell lines, and human tumors.
By using RNase protection analysis, residues 2677 and 2995 of MDR-1 were identified as sites of genetic polymorphism. Through use of oligonucleotide hybridization, the genomic content and expression of individual MDR-1 alleles were examined in normal tissues, unselected and drug selected cell lines, and malignant lymphomas. In normal tissues, unselected cell lines, and untreated malignant lymphoma samples, expression of MDR-1 from both alleles was similar. In contrast, in drug selected cell lines, and in relapsed malignant lymphoma samples, expression of one allele was found in a large percentage of samples. To understand how expression of one allele occurs, two multidrug resistant sublines were isolated by exposing a Burkitt lymphoma cell line to increasing concentrations of vincristine. The resistant sublines expressed only one allele and had a hybrid MDR-1 gene composed of non-MDR-1 sequences proximal to MDR-1. Previous studies showing hybrid MDR-1 genes after rearrangements provided a potential explanation for activation and expression of one MDR-1 allele. We conclude that oligonucleotide hybridization can be used as a sensitive tool to examine relative allelic expression of MDR-1, and can identify abnormal expression from a single allele. Acquired drug resistance in vitro and in patients is often associated with expression of a single MDR-1 allele, and this can be a marker of a hybrid MDR-1 gene.
Mickley
L A
LA
Medicine Branch, Division of Clinical Sciences (DCS), National Cancer Institute (NCI), Bethesda, MD 20892, USA.
Lee
J S
JS
Weng
Z
Z
Zhan
Z
Z
Alvarez
M
M
Wilson
W
W
Bates
S E
SE
Fojo
T
T
D000483:Alleles; D000970:Antineoplastic Agents / Q000494:pharmacology; D001483:Base Sequence; D002051:Burkitt Lymphoma / Q000235:genetics; D004273:DNA, Neoplasm / Q000737:chemistry; D019008:Drug Resistance, Neoplasm; D019450:Genes, MDR / Q000235:genetics*; D006801:Humans; D008223:Lymphoma / Q000188:drug therapy / Q000235:genetics*; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D009841:Oligonucleotides; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D014407:Tumor Cells, Cultured; D014750:Vincristine / Q000494:pharmacology
D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; D009841:Oligonucleotides; D014750:Vincristine